Secure your API communications. Generate Hash-Based Message Authentication Codes instantly using secret keys and MD5, SHA-256, or SHA-512 algorithms.
Easily debug '401 Unauthorized' errors by manually generating perfectly calculated HMAC signatures to compare against your backend logic.
The engine utilizes symmetric mathematics, requiring the exact same Secret Key to generate the signature on the client side and verify it on the server side.
Never paste your AWS or Stripe private keys into a backend tool. Our application executes the Web Crypto API strictly inside your local browser tab to prevent key interception.
APIs have different requirements. The output generates the hexadecimal signature required by traditional REST endpoints, and the Base64 encoding required by JSON Web Tokens.
HMAC (Hash-Based Message Authentication Code) is a specific type of cryptographic algorithm used to secure network communications. By combining a cryptographic hash function (like SHA-256) with a secret cryptographic key, HMAC provides two unbreakable guarantees: Data Integrity (the message wasn't altered) and Authenticity (the message was definitely sent by the person who holds the key).
Imagine you are building a banking app. You want to send an API request to a server to transfer money:
{ "from_account": "John", "to_account": "Bob", "amount": 100 }
If a hacker intercepts this request over a public Wi-Fi network (a Man-In-The-Middle attack), they could easily change the amount to 10,000 and forward it to the server. A basic API has no way of knowing the message was tampered with in transit.
HMAC solves this by attaching a mathematically proven fingerprint to the headers of the API request.
When John sends his request, his app uses a secret key to run the JSON payload through an online HMAC generator algorithm. The resulting signature (e.g., a5f9...) is sent alongside the payload.
If the hacker intercepts the request and changes the amount to 10,000, the JSON payload has changed. When the banking server receives the request, it uses its own copy of the secret key to generate a new HMAC signature based on the tampered payload. Because the payload changed, the server's signature will not match John's original signature. The server immediately throws a 401 Unauthorized error and drops the request.
The most common use case for HMACs in modern software development is securing Webhooks.
event: payment_success so your code can ship the product. However, webhook endpoints are completely public URLs. A hacker can write a script to hit your server with fake "payment success" webhooks, tricking your server into shipping them free products.HMAC-SHA256 signature and attach it to the Stripe-Signature HTTP header.